Patch: Multiple files uploaded

Hi, this is a ready-to-use patch proposal to permit handling of multiple uploaded files within a single field key. https://nopaste.net/wBXKeHXNOp

The patch has no effect on standard functionality but provides compatibility with plugins such as https://www.ads-software.com/plugins/multiline-files-for-contact-form-7/ to store multiple files being uploaded with a single field.

Would you please consider reviewing and applying this patch?

Best regards
Marek Rost